Conventionally, an acrylic fiber having a porous structure in which many voids are present has been is known (Patent Document 1), and a large number of technologies for creating porous structure therein also have been proposed. For example, technologies have been proposed in which a water soluble macromolecular component or an alkaline soluble component is added, and then removed after spinning (Patent Documents 2 and 3).
However, acrylic fibers having porous structure according to such technologies are all intended for improving hygroscopicity and water absorptivity, or for retaining an additive which provides a new function.
[Patent Document 1] Japanese Unexamined Patent Application, Publication No. S63-309613
[Patent Document 2] Japanese Unexamined Patent Application, Publication No. 2003-342831
[Patent Document 3] Japanese Unexamined Patent Application, Publication No. 2007-126794